A conventional Private Branch eXchange (PBX) in local area has packet management interface, switch, and control system for Public Switch Telephone Network (PSTN) circuit and Subscriber Line Interface Circuit (SLIC). The PBX has supervisory system for power supply, and also has an extra route connecting between PSTN circuit and SLIC. The extra route connects PSTN interface and SLIC interface directory. For example, SLIC detects power failure by supervising voltage, and according to the detection, supplies relay driving voltage via control part to switching relay in the PBX. The protection switching is generally provided by switching the direct route.
In Local Area Network (LAN), a LAN switch is connected to data terminals which have 1˜100 Mbps transmission speed via twisted pair cable or optical fiber cable. The LAN switch exchanges Media Access Control (MAC) packet with the terminals via Media Access Control (MAC) layer. The terminals communicate with other terminals in connection less environment wherein MAC address and terminal number are used in stead of circuit switching. Now, voice data communication using internet telephony is becoming popular. Internet telephony call is realized by software using communication protocol.
With the spread of LAN, it will be seen that the PBX and the internet telephony exist together. This means coexistence of networks which have different transmission line and switching method. IP(internet protocol)-PBX is a switching system which communicates integrated voice and data between PSTN and LAN.
Protection switching for power failure in IP-PBX is provided by using extra direct route without LAN switch when the PBX has PSTN interface and SLIC interface including packet processing.